The present invention relates to high strength aluminum base alloys and particularly to wrought high strength aluminum base alloys produced in extruded or hot-rolled plate form, which are well adapted for welding operations in further fabrication steps, wherein the strength properties are retained at high values, even exceeding about 40 ksi for the yield strength of extruded products and 30 ksi for hot rolled plate, without any necessity for interposing special heat treatment steps.
The alloy compositions in accordance with this invention have been shown to meet the specified requirements and have furthermore surprisingly provided excellent solutions to the problems and disadvantages consistently associated with previous attempts to use prior art alloy compositions for such purposes. Such attempts were accompanied by inordinate loss of strength properties on welding, and/or a requirement after welding for special heat treatment and artificial aging steps to recover at least part of the lost strength properties, and/or an excessive tendency to undergo weld failures, such as under-bead weld cracks, and/or susceptibility to various types of corrosion, such as stress corrosion or exfoliation corrosion, which might result in excessive failures in service.
Thus, at least one of the foregoing disadvantages, and usually several of them is encountered in attempts to weld previously known high-strength aluminum base alloys which include magnesium, silicon and copper as essential components, as occurs in such attempted use of AA Alloys 6066 and 6351, and of alloy compositions as disclosed in U.S. Pat. Nos. 3,498,221 and 3,935,007 and in British Pat. No. 1,383,895, also described in Journal of Metals (September, 1976), pages 15-18, which in general were formulated to accomplish purposes differing from the present objectives.
Accordingly, it has been a principal object of the present invention to provide improved high strength aluminum base alloy compositions characterized by the capability of being welded readily without undergoing an excessive decrease in strength properties.
A further object has been the provision of such alloy compositions characterized by the capability of being formed by extrusion or by hot-rolling procedures.
Another object has been the provision of such alloy compositions comprising a defined range of magnesium content in conjunction with other essential elements in proportions required to achieve the desired functional characteristics.
A further object has been the provision of such alloys characterized by heat-treatability and natural aging characteristics.
Another object has been to provide such alloy compositions readily suitable for conversion to wrought products.
Further objects and advantages of the present invention will be apparent from the following detailed description.